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04 Arrays

Learn about arrays, including how to declare, construct, and initialize them. Understand how to manipulate arrays using methods.

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04 Arrays

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  1. 04 Arrays

  2. Outline • What is an array? • Creating arrays • Declaration • Construction • Initialization • Using arrays

  3. Objectives • Define array • Understand different ways to declare an array • Understand different ways to create an array • Understand different ways to initialize arrays • Utilize methods for manipulating arrays

  4. An array is simply a sequence of either objects or primitives, all of the same type and packaged together under one identifier name. type 0 0 0 1 0 2 3 0 Identifier name Indexing operator What is an Array? A one-dimensional array on the heap Values The heap int[] numbers; int [] numbers object Indices int numbers[] ; numbers = new int[4] ;

  5. Creating an Array There are three steps to creating an array: public class Array { public static void main(String[] args) { int[] scores; scores = new int[3]; scores[0] = 10; scores[1] = 7; scores[2] = 9; } } 1. Declaration 2. Construction Initialization 3.

  6. Creating an ArrayDeclaration Declaring an array means providing a name and its data type: public class Array { public static void main(String[] args) { int[] numbers; char[] letters, symbols; long bigNumbers[]; String[] countries; } } Single declaration Multiple declaration Alternative declaration Array of objects

  7. Creating an ArrayConstruction Constructing an array means creating an object of its declared type: public class Array { public static void main(String[] args) { int[] numbers; char[] letters, symbols; long bigNumbers[]; String[] countries; numbers = new int[3]; String[] currencies = new String[3]; } } Create an array of int type consisting of 3 elements Declaration and construction at the same time

  8. Creating an ArrayInitialization Initializing an array means assigning values to its elements: public class Array { public static void main(String[] args) { int[] numbers; char[] letters, symbols; long bigNumbers[]; String[] countries; numbers = new int[3]; String[] currencies = new String[3]; numbers[0]=100; numbers[1]=200; numbers[2]=300; int[] newNumbers = {1,2,3}; } } Array index starts with 0 Declaration, construction, initialization at the same time

  9. Manipulating Arrays public class Array { public static void main(String[] args) { int[] numbers = new int[3]; numbers[0]=100; numbers[1]=200; numbers[2]=300; int[] newNumbers = {1,2,3}; for (int i=0; i<numbers.length; i++) { System.out.println(numbers[i]); } sumNumbers(numbers); sumNumbers(new int[]{3,2,1}); numbers = newNumbers; } static void sumNumbers(int[] n) { int sum=0; for (int i=0; i<n.length; i++) { sum += n[i]; } System.out.println(sum); } } length gives the size of the array Printing each element of an array Passing array to a method Assigning array to another array Passing anonymous array Sample Output 100 200 300 600 6

  10. Key Points • An array is a collection of values (either primitive or objects) all of which have the same data type • There are 3 steps in creating an array: • Declaration • Creation • Initialization • Array elements are accessed using an index that starts at 0 • length is the property of array that returns its size (i.e., number of elements) • Arrays can be passed to methods or assigned to variables

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